Why are there only twelve signs of the zodiac?!

Why are there only twelve signs of the zodiac?

The Julian calendar, introduced by Julius Caesar in 45 BC, began on 1st January, with the length of months alternating between 31 and 30 days - except for February, which had 30 days in a leap year and 29 days otherwise. (This replaced an earlier Roman calendar which had 10 months of alternating 30 and 31 days, followed by a "winter gap", the length of which varied from year to year. The last year of this old calendar actually had 445 days.)

Complications to the Julian system began when the Senate wanted to name a month after the then Emperor Augustus. To avoid slighting the Emperor, the month named for Augustus must be as long as the month named for Julius, and should follow it directly. And so July and August became 31 days each, and February surrendered an extra day. (To avoid 3 successive 31 day months, September was shortened to 30 days, October lengthened to 31, and so on.)

The Romans initially introduced leap years every 3 years, but by about 9 BC it was seen that the calendar was getting out of step with the solstices, so leap years were abandoned altogether, until about AD 4 or 8, when leap years were re-introduced as every 4 years. Even this was not completely accurate, giving an error of 45 minutes in 4 years, or 3 days in 400 years. In time, this miscalculation became quite noticeable.

Around 150 AD Christian churches decided to take over the pagan festival of Saturnalia (the winter solstice) and celebrate 25th December as Christ's birthday. Later, when the cult of the Virgin Mary became popular, it was thought that the Christian era should start on the day of Christ's conception, that is, 9 months earlier on 25th March, which they named Ladyday. The year began on 25th March and ended on the following 24th March.

All moveable feasts in the church calendar relate to Easter. In turn, gospel tradition related Easter to the Jewish festival of Passover, which in turn was related to the spring equinox, the phase of the moon and the celebration of the Sabbath. Over the centuries, by following the Julian calendar, the Easter festival was slowly but surely moving away from the spring equinox towards the summer solstice. The new system adopted by Pope Gregory in the 16th century, specified a calendar with a year length of 365 days, 5 hours, 40 minutes, 20 seconds. Therefore 3 days had to be dropped every 400 years. So those years which were divisible by 100 would only be leap years if they were divisible by 400. To correct errors which had built up over centuries, Pope Gregory declared that Thursday 4th October 1582 in the Julian Calendar should be immediately followed by Friday 15th October in the Gregorian Calendar.

Scotland and most Roman Catholic countries of Europe adopted the Gregorian Calendar in 1582 or soon after. Most Protestant countries however ignored this Papal decision for another 200 years. In England, they still followed the old Julian Calendar (year ending 24th March) until 1751. Lord Chesterfield's Act of 1751/2 stated that the year 1752 would begin on 1st January and end on the following 31 December. In addition, in 1752 only, the calendar was adjusted to omit 11 days (2nd September was followed by 14th September) to bring their "new" (Gregorian) calendar back in line with most of the rest of Europe.

Orthodox countries (those following allegiance to the Patriarch of Constantinople) were even slower to change. Russia, for example, did not convert to the new calendar until after the Russian Revolution. An interesting consequence of this was that when London hosted the 1908 Olympic Games, the Russian team arrived 12 days late because of it! Turkey was the last major European country to adopt the Gregorian Calendar - on 1st January 1927.